Organic semiconducting (OSC) materials are receiving growing interest mostly due to their rapid development in the recent years and the lucrative commercial prospects of organic electronics.
One particular area of importance is organic photovoltaics (OPV). Conjugated polymers have found use in OPVs as they allow devices to be manufactured by solution-processing techniques such as spin casting, dip coating or ink jet printing. Solution processing can be carried out cheaper and on a larger scale compared to the evaporative techniques used to make inorganic thin film devices. Currently, polymer based photovoltaic devices are achieving efficiencies above 8%.
In order to obtain ideal solution-processable OSC molecules two basic features are essential, firstly a rigid π-conjugated core unit to form the backbone, and secondly a suitable functionality attached to the aromatic core unit in the OSC backbone. The former extends π-π overlaps, defines the primary energy levels of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), enables both charge injection and transport, and facilitates optical absorption. The latter further fine-tunes the energy levels and enables solubility and hence processability of the materials as well as π-π interactions of the molecular backbones in the solid state.
A high degree of molecular planarity reduces the energetic disorder of OSC backbones and accordingly enhances charge carrier mobilities. Linearly fusing aromatic rings is an efficient way of achieving maximum planarity with extended π-π conjugation of OSC molecules. Accordingly, most of the known polymeric OSCs with high charge carrier mobilities are generally composed of fused ring aromatic systems and are semicrystalline in their solid states. On the other hand, such fused aromatic ring systems are often difficult to synthesize, and do also often show poor solubility in organic solvents, which renders their processing as thin films for use in OE devices more difficult. Also, the OSC materials disclosed in prior art still leave room for further improvement regarding their electronic properties.
Thus there is still a need for organic semiconducting (OSC) polymers which are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, a good processability, especially a high solubility in organic solvents, and high stability in air. Especially for use in OPV cells, there is a need for OSC materials having a low bandgap, which enable improved light harvesting by the photoactive layer and can lead to higher cell efficiencies, compared to the polymers from prior art.
It was an aim of the present invention to provide compounds for use as organic semiconducting materials that are easy to synthesize, especially by methods suitable for mass production, and do especially show good processability, especially for coating into thick layers, high stability, good solubility in organic solvents, high charge carrier mobility, and a low bandgap. Another aim of the invention was to extend the pool of OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
It was found that one or more of the above aims can be achieved by providing conjugated polymers as disclosed and claimed hereinafter. These polymers comprise repeating units that contain a benzene ring substituted with one or more halogen atoms flanked by silolobithiophene moieties, and a benzofused heteroaromatic moiety flanked by thiophene rings. These novel polymers exhibit good device performance, maintaining a high fill factor with thick coating (with a thickness >150 nm), and excellent environmental stability including thermal and photo stability.
WO 2012/030942 A1 discloses polymers comprising repeating units that contain a fluorinated benzene ring flanked by silolobithiophene moieties, but does not disclose polymers as claimed hereinafter.